This invention relates to a spray dampening system for offset printing presses, and more particularly to a spray dampening system which may be retrofitted on existing offset presses or incorporated into offset press designs and frictionally driven by the plate roll or cylinder. As used herein the term "spray" is intended to include any finely divided form whether in a mist or droplets. The "spraying" may be by means of nozzles or by means of flicker brushes or slinger discs or the like which are well known means for applying the damping fluid to a feed roll.
In the present spray dampening systems for offset printing presses, the dampening fluid is frequently introduced into the ink train usually by spraying directly onto the ink roll or onto dampening rolls which transfer the dampening fluid to the rolls of the ink train. The dampening fluid and ink are thus transferred together to the plate roll and portions of the plate roll are coated with the water-based dampening fluid while the ink is coated on the other portions. In this type of system the dampening and ink rolls are both geared to the printing press rolls.
It is many times preferable to apply the ink and the dampening fluid separately, however, since there is a more even distribution of each. Systems which employ separate ink and dampening fluid trains also are geared to and driven by the press roll drive. The problem is that it is very difficult to retrofit a spray dampening system onto an existing printing press because there is limited room and because it is difficult to gear or otherwise drivingly connect the dampening rolls to the printing press. Heretofore any such dampening system required gearing or belts to tie the dampening system into the printing press drive so that both could be operated at the same speed. Very little effort was made to create a satisfactory frictional drive because of the belief that excessive plate wear would result or inadequate dampening fluid distribution would occur. The object of the spray dampening system is to provide an even distribution of dampening fluid over the surface of the plate cylinder, and it was heretofore believed that it was not possible to achieve this even distribution while providing the frictional engagement necessary to drive the spray dampening system rolls.
Moreover, it has been found that for even distribution, it is desirable to axially reciprocate the water feed rolls. However this adds another obstacle to a satisfactory friction drive system because such axial movement of one roll relative to the other requires axial surface slippage, while for proper frictional drive, the surface slippage, at least in the direction of rotation, should be minimized.
It is an object of this invention to provide a system which can be retrofitted onto existing printing presses and with the distribution roll being frictionally driven by the plate roll of the printing press. By proper selection of the roll materials, axial movement of one roll relative to the other may be accomplished to provide an even distribution of the dampening fluid but the frictional engagement between the rolls will be maintained so that both rolls of the spray dampening system may be driven by friction engagement between one of the rolls and the plate roll of the press.